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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 15/17] errseq: add a new errseq_scrape function [ver #20] From: David Howells To: torvalds@linux-foundation.org, viro@zeniv.linux.org.uk Cc: Jeff Layton , Carlos Maiolino , dhowells@redhat.com, raven@themaw.net, mszeredi@redhat.com, christian@brauner.io, jannh@google.com, darrick.wong@oracle.com, kzak@redhat.com, jlayton@redhat.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 24 Jul 2020 14:37:02 +0100 Message-ID: <159559782287.2144584.13367490538009189134.stgit@warthog.procyon.org.uk> In-Reply-To: <159559768062.2144584.13583793543173131929.stgit@warthog.procyon.org.uk> References: <159559768062.2144584.13583793543173131929.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.23 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: From: Jeff Layton To grab the current value of an errseq_t, mark it as seen and then return the value with the seen bit masked off. Signed-off-by: Jeff Layton Reviewed-by: David Howells Reviewed-by: Carlos Maiolino Signed-off-by: David Howells --- include/linux/errseq.h | 1 + lib/errseq.c | 33 +++++++++++++++++++++++++++++++-- 2 files changed, 32 insertions(+), 2 deletions(-) diff --git a/include/linux/errseq.h b/include/linux/errseq.h index fc2777770768..de165623fa86 100644 --- a/include/linux/errseq.h +++ b/include/linux/errseq.h @@ -9,6 +9,7 @@ typedef u32 errseq_t; errseq_t errseq_set(errseq_t *eseq, int err); errseq_t errseq_sample(errseq_t *eseq); +errseq_t errseq_scrape(errseq_t *eseq); int errseq_check(errseq_t *eseq, errseq_t since); int errseq_check_and_advance(errseq_t *eseq, errseq_t *since); #endif diff --git a/lib/errseq.c b/lib/errseq.c index 81f9e33aa7e7..8ded0920eed3 100644 --- a/lib/errseq.c +++ b/lib/errseq.c @@ -108,7 +108,7 @@ errseq_t errseq_set(errseq_t *eseq, int err) EXPORT_SYMBOL(errseq_set); /** - * errseq_sample() - Grab current errseq_t value. + * errseq_sample() - Grab current errseq_t value (or 0 if it hasn't been seen) * @eseq: Pointer to errseq_t to be sampled. * * This function allows callers to initialise their errseq_t variable. @@ -117,7 +117,7 @@ EXPORT_SYMBOL(errseq_set); * see it the next time it checks for an error. * * Context: Any context. - * Return: The current errseq value. + * Return: The current errseq value or 0 if it wasn't previously seen */ errseq_t errseq_sample(errseq_t *eseq) { @@ -130,6 +130,35 @@ errseq_t errseq_sample(errseq_t *eseq) } EXPORT_SYMBOL(errseq_sample); +/** + * errseq_scrape() - Grab current errseq_t value + * @eseq: Pointer to errseq_t to be sampled. + * + * This function allows callers to scrape the current value of an errseq_t. + * Unlike errseq_sample, this will always return the current value with + * the SEEN flag unset, even when the value has not yet been seen. + * + * Context: Any context. + * Return: The current errseq value with ERRSEQ_SEEN masked off + */ +errseq_t errseq_scrape(errseq_t *eseq) +{ + errseq_t old = READ_ONCE(*eseq); + + /* + * For the common case of no errors ever having been set, we can skip + * marking the SEEN bit. Once an error has been set, the value will + * never go back to zero. + */ + if (old != 0) { + errseq_t new = old | ERRSEQ_SEEN; + if (old != new) + cmpxchg(eseq, old, new); + } + return old & ~ERRSEQ_SEEN; +} +EXPORT_SYMBOL(errseq_scrape); + /** * errseq_check() - Has an error occurred since a particular sample point? * @eseq: Pointer to errseq_t value to be checked.